This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The cyclic nucleotide phosphodiesterase 10A (PDE10A) is highly expressed in the striatum where it participates in signaling mechanisms related to cognitive and motor function. PDE10A is localized to the cell membrane of medium spiny neurons (MSNs) that are the projection neurons driving the striatal output, and hydrolyzes cyclic phosphodiester bonds of cAMP and cGMP, which results in modulation of signal transduction in striatal output pathways. Signaling mechanisms in these pathways are key to the control of posture and movement. In recent years, selective PDE10A inhibitors have been synthesized, and preclinical tests of these agents have shown significant therapeutic potential for schizophrenia. At this time, the effects of these drugs on other realms of behavior are less clear. As with other antipsychotic drugs, it will be particularly important to evaluate the motor effects of PDE10A inhibitors. In this project, we planned to study the effects of MP-10, a selective PDE10A inhibitor on motor behavior and brain metabolic activity in normal macaque monkeys. Knowing such motor effects would not only help us predict potential side effects of the clinical use of these drugs in schizophrenia, but may also lead us to discover alternative applications for PDE10A inhibitors. The project has been extended to evaluate the effects of the common antipsychotic risperidone in the same paradigms for comparison with MP-10. The goal of these studies is to determine the therapeutic advantages of MP-10 with respect to drugs used currently for the therapy of schizophrenia.